Event handling in distributed event handling systems

ABSTRACT

The present disclosure generally discloses an event handling capability configured to support handling of events. The event handling capability may be configured to support handling of events in a distributed event handling system, which may use distributed queuing of events, distributed processing of events, and so forth. The distributed event handling system may be serverless cloud system or other type of distributed event handling system. The event handling capability may be configured to support handling of events in a distributed event handling system based on use of a message bus for queuing of events and based on use of hosts for queuing and processing of events.

TECHNICAL FIELD

The present disclosure relates generally to network technology and, moreparticularly but not exclusively, to event handling in event handlingsystems.

BACKGROUND

Event handling systems may be used to handle various types of eventsthat are associated with various types of services or applications.Event handling systems may be centralized or distributed. Event handlingin distributed event handling systems, such as serverless cloud systemsand other types of distributed event handling systems, may becomplicated.

SUMMARY

The present disclosure generally discloses event handling in eventhandling systems.

In at least some embodiments, an apparatus is provided. The apparatus isconfigured to support handling of events by a message bus of an eventhandling system. The apparatus includes a processor and a memorycommunicatively connected to the processor. The processor is configuredto maintain, by the message bus for an event type, a respective set ofevent queues for the event type, wherein the event queues for the eventtype are associated with respective ones of a set of hosts subscribed tothe message bus for the event type. The processor is configured toreceive, by the message bus for the event type, an event of the eventtype that is published to the message bus. The processor is configuredto store, by the message bus, the event of the event type in one of theevent queues for the event type based on respective sets of queue statusinformation associated with the respective event queues. The processoris configured to send, by the message bus, the event of the event typetoward one of the hosts subscribed to the message bus for the event typebased on a request from the one of the hosts subscribed to the messagebus for the event type. In at least some embodiments, a non-transitorycomputer-readable storage medium stores instructions which, whenexecuted by a computer, cause the computer to perform a correspondingmethod for supporting handling of events by a message bus of an eventhandling system. In at least some embodiments, a corresponding methodfor supporting handling of events by a message bus of an event handlingsystem is provided.

In at least some embodiments, an apparatus is provided. The apparatus isconfigured to support handling of events by a host of an event handlingsystem. The apparatus includes a processor and a memory communicativelyconnected to the processor. The processor is configured to subscribe, bythe host, to a first event queue of a message bus, the first event queueof the message bus configured to store events of a first event type tobe processed by a first event processing function of the host. Theprocessor is configured to subscribe, by the host, to a second eventqueue of the message bus, the second event queue configured to storeevents of a second event type to be processed by a second eventprocessing function of the host. The processor is configured tomaintain, by the host, a local buffer configured to store eventsreceived from the first event queue of the message bus and eventsreceived from the second event queue of the message bus. The processoris configured to retrieve, by the host based on a local queuing policyof the host and a local event retrieval condition detected at the host,a retrieved event comprising a first event from the first event queue ofthe message bus or a second event from the second event queue of themessage bus. In at least some embodiments, a non-transitorycomputer-readable storage medium stores instructions which, whenexecuted by a computer, cause the computer to perform a correspondingmethod for supporting handling of events by a host of an event handlingsystem. In at least some embodiments, a corresponding method forsupporting handling of events by a host of an event handling system isprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings herein can be readily understood by considering thefollowing detailed description in conjunction with the accompanyingdrawings, in which:

FIG. 1 depicts an event handling system configured to supportdistributed handling of events;

FIG. 2 depicts an event handling system configured to supportdistributed handling of events;

FIG. 3 depicts an embodiment of a method for use by a message bus tosupport event handling;

FIG. 4 depicts an embodiment of a method for use by a host to supportevent handling;

FIG. 5 depicts an event handling system configured to supportdistributed handling of events based on a distributed message bus; and

FIG. 6 depicts a high-level block diagram of a computer suitable for usein performing various functions presented herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

The present disclosure generally discloses an event handling capabilityconfigured to support handling of events. The event handling capabilitymay be configured to support handling of events in a distributed eventhandling system, which may use distributed queuing of events,distributed processing of events, and so forth. The distributed eventhandling system may be serverless cloud system or other type ofdistributed event handling system. It will be appreciated that these andvarious other embodiments and advantages or potential advantages of theevent handling capability may be further understood by way of referenceto the example event handling system of FIG. 1.

FIG. 1 depicts an event handling system configured to supportdistributed handling of events.

The event handling system 100 includes a communication system 110, a setof hosts 120-1-120-N (collectively, hosts 120), and a management system(MS) 130.

The communication system 110 may be any type of communication systemconfigured to support communications of the hosts 120 (e.g.,communication of event processing requests entering the event processingsystem 100 from external sources, communication of events from ones ofthe hosts 120 operating as publishers of the events, communication ofevents to ones of the hosts 120 operating as subscribers to the events,communication of event processing responses from hosts 120 based onprocessing of events by the hosts 120, or the like, as well as variouscombinations thereof) and communications of the MS 130 (e.g.,communication of events being exchanged between hosts 120, communicationof management messages associated with scaling of the hosts 120, or thelike, as well as various combinations thereof).

The communication system 110 may be a communication network (e.g., awireline network, a wireless network, or the like, as well as variouscombinations thereof), a messaging system, or the like, as well asvarious combinations thereof.

The hosts 120 may be any types of hosts configured to support handlingof events. The hosts 120 may be configured to be publishers of events,subscribers to events, or both. For example, the hosts may be physicalhosts (e.g., servers), virtual hosts (e.g., virtual machines (VMs),virtual containers (VCs), or the like), or the like, as well as variouscombinations thereof). The hosts 120 may be distributed in various ways(e.g., physical hosts that are geographically distributed, virtual hoststhat are distributed across physical servers, or the like, as well asvarious combinations thereof).

The MS 130 is configured to support distributed handling of events. TheMS 130 includes a message bus (MB) 131 configured to controldistribution of events across the hosts 120 and a function manager (FM)132 configured to control scaling of hosts 120 supporting processing ofevents. The MB 131 may be configured to control distribution of eventsacross the hosts 120 based on monitoring of queues of the MB 131 thatare used to distribute events across the hosts 120, where the dynamicsof the queues of the MB 131 that are used to distribute events acrossthe hosts 120 may be based on backpressure resulting at the MB 131 fromlocal handling of respective queues on the respective hosts 120 (e.g.,each of the hosts 120 is able to locally and independently determine itslevel of participation in processing of events in a manner that enablesthe MB 131 to intelligently control distribution of events across thehosts 120 without the use of explicit feedback from the hosts 120). TheFM 132 may be configured to control scaling of hosts 120 supportingprocessing of events based on feedback from the MB 131, supporting scaleout and scale in of hosts 120 for event types. It will be appreciatedthat, although primarily presented with respect to embodiments in whichthe MB 131 and the FM 132 are part of a particular element (namely, MS130), the MB 131 and the FM 132 may be standalone elements, may bedistributed across various elements, or the like, as well as variouscombinations thereof.

The event handling system 100 may be a serverless cloud system. In aserverless cloud system, which also may be referred to as afunction-as-a-service (FaaS) cloud resources are utilized based ondemand from the applications and services with the clients being chargedbased on the amount of resources consumed and with the management ofthose resources being transparent or substantially transparent to theclients. In a serverless cloud system, the applications or servicesgenerally follow an event-driven programming model in which the eventprocessing functions of the application or service are triggered byevents within the serverless cloud system (e.g., a specific web browsingaction by an end user, uploading of an image to a storage server, or thelike). In a serverless cloud system, the handling of a request to theapplication or service in order to provide an associated response fromthe application or service may be based on a graph of event processingfunctions that is configured to handle respective events associated withproviding the response to the request, where the graph of eventprocessing functions may be distributed across the resources in variousways. For example, the event processing functions may be distributedacross hosts 120 in various ways, such that the hosts 120 may exchangeevents in order to support completion of the response to the request(e.g., an output based on processing of an event by an event processingfunction of a host 120 may be provided as an input event to be processedby that host 120 and/or one or more other hosts 120). It will beappreciated that the event handling system 100 may be any other suitabletype of event handling system in which events may be processed (e.g., atraditional cloud system in which clients request virtual resources tobe used to handle processing of events or the like); however, variousembodiments of the event handling capability are primarily presentedherein within the context of a serverless cloud system.

The event handling system 100 is configured to support distributedhandling of events. The events may be events of one or more applicationsor services supported by the event handling system 100. The events maybe external arriving at the event handling system 100 from one or moreexternal source of the events (e.g., requests from clients, requestsfrom network devices, or the like), internal events generated within theevent handling system 100 by one or more hosts 120 of the event handlingsystem 100 (e.g., as discussed above, outputs by hosts 120 based onprocessing of events by event processing functions of the hosts 120 maybe inputs, or events, to be processed by hosts 120), or the like, aswell as various combinations thereof. The events may include events ofone or more event types (e.g., multiple event types associated withrespective applications or services, multiple event types supported by agiven application or service, or the like, as well as variouscombinations thereof). For example, where the event handling system 100supports a database service, events of a first event type may berequests to retrieve data from the database and events of a second eventtype may be requests to write data in the database. For example, wherethe event handling system supports a web browsing service, events mayinclude external events (e.g., requests from clients) and internalevents (e.g., requests for respective pieces of information to beassembled in order to return associated responses to the clients andprocessing to assemble the respective pieces of information in order toreturn associated responses to the clients). It will be appreciated thatthe event handling system 100 may be configured to handle various othertypes of events, applications or services, or the like, as well asvarious combinations thereof.

It will be appreciated that the event handling system 100, althoughprimarily presented as being organized in a particular manner, may beorganized in various other ways (e.g., using other numbers, types, orarrangements of communication systems, using other numbers, types, orarrangement of hosts, or the like, as well as various combinationsthereof).

FIG. 2 depicts an event handling system configured to supportdistributed handling of events.

The event handling system 200 is configured to support handling ofevents. The event handling system 200 is depicted as being associatedwith a single cloud node or cloud location; however, the event handlingsystem 200 may be associated with multiple cloud nodes or cloudlocations.

The event handling system 200 is configured to support handling of twoevent types (primarily referred to herein as event type A and event typeB). The two event types may be associated with a common service orapplication supported by the event handling system 200 (e.g., theservice or application may require or support handling of the two eventtypes), may be associated with two respective services or applicationssupported by the event handling system 200 (e.g., a first service orapplication requires or supports handling of events of event type A anda second service or application requires or supports handling of eventsof event type B), may be associated with multiple services orapplications supported by the event handling system 200 (e.g., eachservice or application may require or support handling of events of oneor more of the event types), or the like, as well as variouscombinations thereof. It will be appreciated that the event handlingsystem, although primarily presented with respect to handling of twoevent types, may be configured to handle any number of event types forany number of services or applications.

The event handling system 200 includes a message bus (MB) 210, a pair ofhosts 220-1 and 220-2 (collectively, hosts 220), and a function manager(FM) 230. It will be appreciated that, although only two hosts 220 aredepicted, fewer or more hosts 220 may be used (and, further that thenumber of hosts 220 used may be controlled dynamically). The MB 210 isconfigured to support queueing of events for the hosts 220 while theevents are awaiting processing by the hosts 220. The hosts 220 areconfigured to subscribe to the MB 210 to receive events from the MB 210.The hosts 220 are configured to receive events from the MB 210 andprocess the events from the MB 210. The FM 230 is configured to controlconfiguration and scaling of the hosts 220 for supporting processing ofevents.

The MB 210 is configured to manage events that are awaiting processingby the hosts 220. The MB 210 is configured to receive events that are tobe processed by the hosts 220. The MB 210 may receive events based onpublication of the events to the MB 210 (e.g., by hosts 220, by one ormore other hosts (not presented in FIG. 2), by one or more other sourcesof events (not presented in FIG. 2), or the like, as well as variouscombinations thereof). The MB 210 is configured to provide events to thehosts 220 responsive to requests by the hosts 220 to pull the events tothe host 220.

The MB 210 includes an event dispatcher (ED) 211, a set of event queues(EQs) 212 (collectively, EQs 212), and a queue monitor (QM) 213.

The ED 211 is configured to receive events and dispatch the events tothe EQs 212 for storage in the EQs 212 while the events await processingby the hosts 220. The ED 211 may receive events based on publication ofthe events to the MB 210. The ED 211 may be configured to determinequeuing of events in the EQs 212. The ED 211 may be configured todetermine queuing of events in the EQs 212 based on event typeinformation of the events that are received (e.g., an event of an eventtype is queued within one of the EQs 212 of that event type). The ED 211may be configured to determine queuing of events in the EQs 212 based onqueue status information of the EQs 212 that is received from the QM213. The queue status information may include various metrics which maybe determined by the QM 213 based on monitoring of the EQs 212 by the QM213. For example, the queue status information for an EQ 212 may includeone or more of a queue length (L) of the EQ 212, an arrival rate (λ) ofthe EQ 212, a departure rate (μ) of the EQ 212, an expected queuewaiting time (E(dt)) for an arriving event at the EQ 212, a change of aqueue length (L) of the EQ 212 over a time interval (dL/dt), or thelike, as well as various combinations thereof. The ED 211 may beconfigured to receive an event, determine an event type of the event,and determine queuing of the event in the EQs 212 based on the queuestatus information of the EQs 212 configured to store events of thatevent type (as discussed further below, EQs 212 correspond tocombinations of event types and hosts).

The ED 211 may be configured to queue events in the EQs 212 based onvarious portions or combinations of the queue status information of theEQs 212 which may be determined based on monitoring of the EQs 212 by QM213. For example, the ED 211 may be configured to queue an event basedon queue lengths (L) of the EQs 212 that are associated with the eventtype of that event (e.g., ED 211, for an event of a particular eventtype, may be configured to dispatch the event to one of the EQs 212,associated with that event type, having a shortest queue length (L)).For example, the ED 211 may be configured to queue an event based onexpected queue waiting times (E(dt)) of the EQs 212 that are associatedwith the event type of that event (e.g., ED 211, for an event of aparticular event type, may be configured to dispatch the event to one ofthe EQs 212, associated with that event type, having a shortest expectedqueue waiting time (E(dt)). The ED 211 may be configured to queue eventsin the EQs 212 based on various other portions or combinations of thequeue status information of the EQs 212 which may be determined based onmonitoring of the EQs 212 by QM 213.

The ED 211 may be configured to queue an event based on queue scores ofthe EQs 212 that are associated with the event type of that event. TheED 211 may be configured to determine queue scores for the EQs 212 of anevent type based on various portions or combinations of the queue statusinformation of the EQs 212, respectively. The queue scores for the EQs212 of an event type may be configured to enable the ED 211 to select anEQ 212 having a longer queue length over an EQ 212 having a shorterqueue length when the queue length of the EQ 212 having the longer queuelength and the queue length of the EQ 212 having the shorter queuelength are changing at different rates (e.g., where the EQ 212 havingthe shorter queue length is draining more slowly than the EQ 212 havingthe longer queue length). The ED 211 may be configured to compute thequeue score (S) of an EQ 212 based on the queue length (L) of the EQ 212and the arrival rate (λ) of the EQ 212. The ED 211 may be configured tocompute the queue score (S) of an EQ 212 based on the queue length (L)of the EQ 212 and the departure rate (μ) of the EQ 212. For example, theED 211 may be configured to compute the queue score (S) of an EQ 212using exponentially weighted moving averages of queue length (L) anddeparture rate (μ) as follows: S=EWMA(μ)/EWMA(L), in which case thequeue score is inversely proportional to an estimated waiting time ofthe event in the EQ 212. It will be appreciated that, although primarilydiscussed with respect to embodiments in which EWMA is used forsmoothing, other types of averaging functions may be used for smoothing.The ED 211 may be configured to compute the queue scores of the EQs 212based on various other portions or combinations of the queue statusinformation of the EQs 212 which may be determined based on monitoringof the EQs 212 by QM 213 (e.g., using one or more of a queue length (L)of the EQ 212, an arrival rate (λ) of the EQ 212, a departure rate (μ)of the EQ 212, an expected queue waiting time (E(dt)) for an arrivingevent at the EQ 212, a change of a queue length (L) of the EQ 212 over atime interval (dL/dt), or the like, as well as various combinationsthereof).

The ED 211 may be configured to support various other functions forreceiving events and dispatching the events to the EQs 212 for storagein the EQs 212 while the events await processing by the hosts 220.

The EQs 212 are configured to receive events from the ED 211 and tostore the events while the events await processing by hosts 220. The EQs212 are configured to allow for addressing based on a combination ofevent type and host. Namely, the set of EQs 212 includes, for each ofthe event types, a respective EQ 212 for each of the hosts 220 that issubscribed to handle events of that respective event type. Morespecifically, the set of EQs 212 includes (1) a first pair of EQs 212-A1and 212-A2 for event type A (collectively, EQs 212-A for event type A),where the EQ 212-A1 is maintained by the MB 210 for queuing events ofevent type A for host 220-1 and the EQ 212-A2 is maintained by the MB210 for queuing events of event type A for host 220-2 and (2) a secondpair of EQs 212-B1 and 212-B2 for event type B (collectively, EQs 212-Bfor event type B), where the EQ 212-B1 is maintained by the MB 210 forqueuing events of event type B for host 220-1 and the EQ 212-B2 ismaintained by the MB 210 for queuing events of event type B for host220-2. The EQs 212 are configured to provide queued events to the hosts220 responsive to requests from the hosts 220 (e.g., host 220-1 mayrequest events of event type A from EQ 212-A1 and may request events ofevent type B from EQ 212-B1 and host 220-2 may request events of eventtype A from EQ 212-A2 and may request events of event type B from EQ212-B2). It will be appreciated that, although primarily presented withrespect to a situation in which both of the hosts 220 are subscribed tohandle both of the event types, each of the hosts 220 may be subscribedto handle one or more event types, the hosts 220 may be subscribed tohandle different sets of event types (e.g., host 220-1 may be subscribedto handle events of event type A and event type B whereas host 220-2 maybe subscribed to handle events of event type B only), or the like, aswell as various combinations thereof.

The QM 213 is configured to monitor the EQs 212 for use in supportinghandling of events (e.g., for supporting ED 211 in controllingdistribution of events to the EQs 212, for supporting FM 230 incontrolling scaling of the hosts 220 for supporting processing ofevents, or the like, as well as various combinations thereof). The QM213 may be configured to, for each of the EQs 212, determine queuestatus information of the EQ 212 based on monitoring of the EQ 212(e.g., monitoring the queue length (L) of the EQ 212, monitoring themanner in which events move through the EQ 212 (e.g., monitoring thearrival rate (λ) of events to the EQ 212, monitoring the departure rate(μ) of events from the EQ 212, or both), or the like, as well as variouscombinations thereof). The queue status information for an EQ 212 mayinclude a queue length (L) of the EQ 212, an arrival rate (λ) of eventsto the EQ 212, a departure rate (μ) of events from the EQ 212, anexpected queue waiting time (E(dt)) for an arriving event at the EQ 212,a change of a queue length (L) of the EQ 212 over a time interval(dL/dt), or the like, as well as various combinations thereof. The QM213 may be configured to compute an expected queue waiting time (E(dt))for an arriving event at an EQ 212 by assuming that the estimateddeparture rate (μ) of the EQ 212 is not changing significantly beforethe event leaves the EQ 212: E(dt)=L/μ. The QM 213, assuming or undercertain conditions, may be configured to estimate a queue statusparameter based on monitoring and measurement of other queue statusparameters (e.g., assuming that the event arrival and departure rateschange only slowly so that both are approximately constant over a shorttime interval dt, then it is possible to measure the change of queuelength dL over the same interval dt and relate the metrics as follows:dL/dt=λ−μ (such that, by measuring two of the three values, the thirdvalue may be estimated)). The QM 213 may be configured to determinevarious other types of queue status information for the EQs 212 based onmonitoring of the EQs 212. The QM 213 may be configured to provide thequeue status information of the EQs 212 to the ED 211 for use incontrolling queueing of events in the EQs 212. The QM 213 may beconfigured to provide the queue status information of the EQs 212 to theFM 230 for use in determining scaling of the hosts 220. The QM 213 alsomay be configured to determine per-host queuing information for thehosts 220 (e.g., over the sets of EQs 212 associated with the hosts 220)and provide the per-host queuing information to the FM 230 for use indetermining scaling of the hosts 220.

The hosts 220 are configured to support handling of events. The hosts220 are configured to support configuration of the hosts 220 to supportevent handling (e.g., obtaining event processing function capabilitiesfor respective event types to be supported by the respective hosts 220,subscribing to event types to be supported by the respective hosts 220,configuring the hosts 220 to be able to store events to be processed atthe hosts 220, or the like, as well as various combinations thereof),pull events from the MB 210 for event types supported by the respectivehosts 220, queue the events pulled from the MB 210 for event typessupported by the respective hosts 220, and process the events pulledfrom the MB 210 for event types supported by the respective hosts 220.

The hosts 220 include respective sets of elements configured to enablethe hosts 220 to support handling of events. The hosts 220 includerespective event buffers 221 (illustratively, the host 220-1 includes anevent buffer 221-1 and host 220-2 includes an event buffer 221-2, whichare local buffers local to the hosts 220-1 and 220-2, respectively)configured to store events retrieved by the hosts 220 for processing bythe hosts 220, respectively. The hosts 220 include respective processingelements 225 (illustratively, the host 220-1 includes a processingelement 225-1 and the host 220-2 includes a processing element 225-2)configured to enable the hosts 220 to provide various functionsdiscussed herein (e.g., configuration of the hosts 220 to support eventhandling, pulling events from the MB 210 for event types supported bythe respective hosts 220, queuing the events pulled from the MB 210 forevent types supported by the respective hosts 220, processing the eventspulled from the MB 210 for event types supported by the respective hosts220, or the like, as well as various combinations thereof). The hosts220 include respective storage elements 226 (illustratively, the host220-1 includes a storage element 226-1 and the host 220-2 includes astorage element 226-2) storing host-specific event pulling/queuingpolicies 227 of the hosts 220 (illustratively, the storage element 226-1of host 220-1 stores a host-specific event pulling/queuing policy 227-1of the host 220-1 and the storage element 226-2 of host 220-2 stores ahost-specific event pulling/queuing policy 227-2 of the host 220-2),host-specific event selection policies 228 (illustratively, the storageelement 226-1 of host 220-1 stores a host-specific event selectionpolicy 228-1 of the host 220-1 and the storage element 226-2 of host220-2 stores a host-specific event selection policy 228-2 of the host220-2), and event processing functions 229 (illustratively, the storageelement 226-1 of the host 220-1 stores an event processing function229-1A configured to be executed by the processing element 225-1 of thehost 220-1 to process events of event type A and an event processingfunction 229-1B configured to be executed by the processing element225-1 of the host 220-1 to process events of event type B and thestorage element 226-2 of the host 220-2 stores an event processingfunction 229-2A configured to be executed by the processing element225-2 of the host 220-2 to process events of event type A and an eventprocessing function 229-2B configured to be executed by the processingelement 225-2 of the host 220-2 to process events of event type B). Theoperation of the hosts 220 in supporting handling of events receivedfrom MB 210 is discussed further below.

The hosts 220 are configured to support configuration of the hosts 220to support event handling. A host 220 may be configured to support eventhandling for events of a particular event type by obtaining the eventprocessing function 229 that is configured to support processing ofevents of the particular event type, subscribing to the MB 210 for theparticular event type such that the host 220 may retrieve events of theparticular event type from MB 210 based on the host-specific eventpulling/queuing policy 227 of the host 220, configuring the event buffer221 of the host 220 to support storage of events of the particular eventtype at the host 220, or the like, as well as various combinationsthereof. A host 220 may be configured to support event handling forevents of a particular event type responsive to a request by the FM 230for the host 220 to handle events of the particular event type. It isnoted that the various functions used to configure a host 220 to supportevent handling for events of a particular event type may be performedwith various timings (e.g., serially, contemporaneously, or the like),responsive to various conditions, or the like, as well as variouscombinations thereof. For example, a host 220 may, responsive to arequest by the FM 230 for the host 220 to handle events of a particularevent type, obtain the event processing function 229 that is configuredto support processing of events of the particular event type andsubscribe to the MB 210 for the particular event type such that the host220 may retrieve events of the particular event type from MB 210. Forexample, a host 220 may obtain the event processing function 229 that isconfigured to support processing of events of the particular event typeresponsive to a request by the FM 230 for the host 220 to handle eventsof the particular event type, subscribe to receive events of theparticular event type from MB 210 responsive to a determination that thehost 220 has obtained the event processing function 229 that isconfigured to support processing of events of the particular event type,and so forth. For example, a host 220 may obtain the event processingfunction 229 that is configured to support processing of events of theparticular event type responsive to a request by the FM 230 for the host220 to handle events of the particular event type, configure the eventbuffer 221 of the host 220 to support storage of events of theparticular event type at the host 220 responsive to a determination thatthe host 220 has obtained the event processing function 229 that isconfigured to support processing of events of the particular event type,subscribe to receive events of the particular event type from MB 210responsive to a determination that the host 220 has configured the eventbuffer 221 of the host 220 to support storage of events of theparticular event type at the host 220, and so forth. It will beappreciated that configuration of a host 220 to support event handlingmay be performed in other ways (e.g., using various other timings,responsive to various other conditions, or the like, as well as variouscombinations thereof).

The hosts 220 are configured to pull events from the MB 210 and queueevents pulled from the MB 210. The hosts 220 may be configured tolocally control pulling/queuing of events from the EQs 212 of the MB 210subscribed to by the hosts 220. The hosts 220 may be configured tolocally control pulling/queuing of events from the EQs 212 of the MB 210subscribed to by the hosts 220 based on the host-specific eventpulling/queuing policies 227 of the hosts 220, respectively. Thehost-specific event pulling/queuing policies 227, as presented in FIG.2, may be different for the hosts 220. Namely, as presented in FIG. 2,(1) the host 220-1 uses an event buffer 221-1 that includes a pair ofhost event queues (HEQs) 222-A and 222-B (collectively, HEQs 222)configured to store events of event type A and events of event type B,respectively and (2) the host 220-2 uses an event buffer 221-2 that isimplemented as a first-in-first-out (FIFO) buffer configured to storeevents of event type A and events of event type B. The host-specificevent pulling/queuing policies 227, although omitted from FIG. 2 forpurposes of clarity, may be the same for the hosts 220. The hosts 220may be configured to locally control pulling/queuing of events from theEQs 212 of the MB 210 subscribed to by the hosts 220 based on localevent retrieval conditions detected at the hosts 220. For example, for agiven host 220, the local event retrieval condition(s) detected at thehost 220 may include detection that a current load at the host 220satisfies a threshold, detection of a characteristic(s) of eventsalready pulled from the MB 210 by the host 220 or events available to bepulled from the MB 210 by the host 220, detection of one or morecapabilities of the host 220, or the like, as well as variouscombinations thereof. The local event retrieval conditions detected atthe hosts 220 may be detected based on host-specific informationavailable at the hosts 220, respectively. For example, the host-specificinformation available at the hosts 220 may include current load levelsat the hosts 220, one or more characteristics of events already pulledfrom the MB 210 by the hosts 220 or events available to be pulled fromthe MB 220 by the hosts 220, or the like, as well as variouscombinations thereof. The hosts 220 may be configured to locally controlpulling/queuing of events from the EQs 212 of the MB 210 subscribed toby the hosts 220 based on local event retrieval conditions detected atthe hosts 220 using various combinations of local event retrievalconditions, host-specific information, or the like, as well as variouscombinations thereof. For example, a host 220 may decide to pullmemory-hungry events from MB 210 when the host 220 is CPU bottlenecked,may decide to pull CPU-hungry events from the MB 210 when the host 220is memory bottlenecked, or the like. In this manner, decisions by thehost 220 regarding pulling/queuing of events from the EQs 212 of the MB210 remain local to the hosts 220 such that they do not need to becommunicated between the hosts 220 and, thus, do not require anycommunication or coordination between the hosts 220 for this purpose. Itis noted that local decisions of the hosts 220 in pulling/queuing eventsfrom the MB 210 produce backpressures on the EQs 212 in the MB 210,which are monitored and summarized in the queue status information ofthe EQs 212 (e.g., the queue lengths and associated queue dynamics).

The hosts 220 are configured to process events queued at the hosts 220.The hosts 220 process events by retrieving events from the event buffers221 based on the host-specific event selection policies 228 andprocessing the events using the event processing functions 229.

The hosts 220 are configured to retrieve events from the event buffers221 for processing by the hosts 220. The hosts 220 may be configured tolocally control selection of events from the event buffers 221 of thehosts 220. The hosts 220 may be configured to locally control selectionof events from the event buffers 221 of the hosts 220 based on thehost-specific event selection policies 228 of the hosts 220,respectively. The host-specific event selection policies 228 may bedifferent for the hosts 220, may be the same for the hosts 220, or thelike. The host-specific event selection policies 228 of the host 220 maybe at least partially based on the host-specific event pulling/queuingpolicies 227 of the hosts (e.g., the manner in which events are selectedfor processing at host 220-1 may be at least partially based on the factthat the host 220-1 maintains separate HEQs 222 for queuing of differentevent types, the manner in which events are selected for processing athost 220-2 may be at least partially based on the fact that the host220-2 maintains a single FIFO queue for queuing of different eventtypes, and so forth). For example, host 220-1 may be configured toselect between processing events of event type A and processing eventsof event type B since the host 220-1 uses the event buffer 221-1 thatincludes the HEQs 222-A and 222-B configured to store events of eventtype A and events of event type B, respectively. For example, host 220-2may be configured to process events of event type A and events of eventtype B based on the ordering of the events within the event buffer 221-2since the event buffer 221-2 is implemented as a FIFO buffer. The hosts220 may be configured to locally control selection of events from theevent buffers 221 of the hosts 220 based on host-specific informationavailable at the hosts 220, such as host resources available at thehosts 220, host resources needed for processing events at the hosts 220,one or more characteristics of events awaiting processing by the hosts220, or the like, as well as various combinations thereof. For example,a host 220 may decide to process memory-hungry events when the host 220is CPU bottlenecked, may decide to process CPU-hungry events when thehost 220 is memory bottlenecked, or the like. The hosts 220 may beconfigured to locally control selection of events from the event buffers221 of the hosts 220 based on the host-specific event selection policies228 and local event selection conditions detected at the hosts 220(e.g., a current load at a host being below a threshold, detection of aparticular characteristic of events awaiting processing by the hosts220, or the like, as well as various combinations thereof). In thismanner, decisions by the host 220 regarding processing of events from MB210 at the hosts 220 remain local to the hosts 220 such that they do notneed to be communicated between the hosts 220 and, thus, do not requireany communication or coordination between the hosts 220 for thispurpose.

The hosts 220 are configured to process the events, retrieved from theevent buffers 221, using the event processing functions 229 available onthe hosts 220. For example, the host 220-1 is configured to (1) processevents of event type A, which are retrieved from the HEQ 222-A of host220-1 based on the host-specific event selection policy 228-1 of thehost 220-1, based on execution of the event processing function 229-1Aby the processing element 225-1 of the host 220-1 and (2) process eventsof event type B, which are retrieved from the HEQ 222-B of host 220-1based on the host-specific event selection policy 228-1 of the host220-1, based on execution of the event processing function 229-1B by theprocessing element 225-1 of the host 220-1. Similarly, for example, thehost 220-2 is configured to (1) process events of event type A, whichare retrieved from the event buffer 221-2 of host 220-2 based on thehost-specific event selection policy 228-2 of the host 220-2, based onexecution of the event processing function 229-2A by the processingelement 225-2 of the host 220-2 and (2) process events of event type B,which are retrieved from the event buffer 221-2 of host 220-2 based onthe host-specific event selection policy 228-2 of the host 220-2, basedon execution of the event processing function 229-2B by the processingelement 225-2 of the host 220-2. The processing of the events by thehosts 220 may trigger various related actions (e.g., storage or sendingof state information, storage or sending of processing results, storageor sending of processing responses, or the like, as well as variouscombinations thereof) which may vary based on various factors (e.g., theservice or application being supported, event types of the events, orthe like, as well as various combinations thereof. The hosts 220 areconfigured to control processing of events locally at the hosts 220 suchthat the processing of events by the hosts 220 does not require anycommunication or coordination between the hosts 220. The hosts 220 eachmay be configured to monitor their own resource usages locally and toapply allocation policies suitable for utilizing the local resources ofthe hosts 220, with the monitoring and allocation of any particular host220 being independent of other hosts 220. In this manner, decisions bythe hosts 220 regarding processing of events at the hosts 220 remainlocal to the hosts 220 such that they do not need to be communicatedbetween the hosts 220 and, thus, do not require any communication orcoordination between the hosts 220 for this purpose.

The FM 230 is configured to control configuration and scaling of thehosts 220 for supporting processing of events. The FM 230 may beconfigured to control configuration of the hosts 220 for supportingprocessing of events (e.g., requesting or instructing hosts 220 toobtain event processing functions 229 for particular event types, tosubscribe to the MB 210 for particular event types, or the like, as wellas various combinations thereof). The scaling may include scale out orscale in of the hosts 220. The scaling of hosts 220 may includeconfiguration of existing hosts 220, instantiation of new hosts 220,termination of existing hosts 220, or the like, as well as variouscombinations thereof. The configuration of existing hosts 220 mayinclude configuring a host 220 to support processing of an event type(e.g., requesting or instructing the host 220 to obtain the eventprocessing function 229 for the event type and to subscribe to receiveevents of that event type from the MB 210 such that the MB 210instantiates an EQ 212 for that host 220 for that event type),configuring a host 220 to stop supporting processing of an event type(e.g., requesting or instructing the host 220 to remove the eventprocessing function 229 for the event type and to unsubscribe fromreceiving events of that event type from the MB 210 such that the MB 210removes the EQ 212 for that host 220 for that event type), or the like,as well as various combinations thereof. The FM 230 may be configured tocontrol scaling of the hosts 220 for supporting processing of eventsbased on information received form the QM 213 of MB 210 (e.g., queuestatus information of the EQs 212, per-host queuing information of thehosts 220, or the like, as well as various combinations thereof).

It will be appreciated that the event handling system 200, althoughprimarily presented as being organized in a particular manner, may beorganized in various other ways (e.g., using other numbers, types, orarrangements of hosts or host capabilities, message bus capabilities, orthe like, as well as various combinations thereof).

FIG. 3 depicts an embodiment of a method for use by a message bus tosupport event handling. It will be appreciated that, although primarilypresented herein as being performed serially, at least a portion of thefunctions of method 300 may be performed contemporaneously or in adifferent order than as presented in FIG. 3.

At block 301, method 300 begins.

At block 310, maintain, by the message bus for an event type, arespective set of event queues for the event type, wherein the eventqueues for the event type are associated with respective ones of a setof hosts subscribed to the message bus for the event type.

At block 320, receive, by the message bus for the event type, an eventof the event type that is published to the message bus.

At block 330, store, by the message bus, the event of the event type inone of the event queues for the event type based on respective sets ofqueue status information associated with the respective event queues.

At block 340, send, by the message bus, the event of the event typetoward one of the hosts subscribed to the message bus for the event typebased on a request from the one of the hosts subscribed to the messagebus for the event type.

At block 399, method 300 ends.

FIG. 4 depicts an embodiment of a method for use by a host to supportevent handling. It will be appreciated that, although primarilypresented herein as being performed serially, at least a portion of thefunctions of method 400 may be performed contemporaneously or in adifferent order than as presented in FIG. 4.

At block 401, method 400 begins.

At block 410, subscribe, by the host, to a first event queue of amessage bus, the first event queue of the message bus configured tostore events of a first event type to be processed by a first eventprocessing function of the host.

At block 420, subscribe, by the host, to a second event queue of themessage bus, the second event queue configured to store events of asecond event type to be processed by a second event processing functionof the host.

At block 430, maintain, by the host, a local buffer configured to storeevents received from the first event queue of the message bus and eventsreceived from the second event queue of the message bus.

At block 440, retrieve, by the host based on a local queuing policy ofthe host and a local event retrieval condition detected at the host, aretrieved event comprising a first event from the first event queue ofthe message bus or a second event from the second event queue of themessage bus.

At block 499, method 400 ends.

It will be appreciated that, although primarily presented with respectto embodiments in which the event handling system includes a centralizedmessage bus (illustratively, MB 210 of event handling system 200), in atleast some embodiments the event handling system may include adistributed message bus. An example of an event handling system using adistributed message bus is presented in FIG. 5.

FIG. 5 depicts an event handling system configured to supportdistributed handling of events based on a distributed message bus.

The event handling system 500 is configured to support handling ofevents. The event handling system 500 is depicted as being associatedwith two cloud nodes or cloud locations; however, the event handlingsystem 500 may be associated with a single cloud node or cloud location.

The event handling system 500 is configured to support handling of twoevent types (primarily referred to herein as event type A and event typeB).

The event handling system 500 includes a global message bus (GMB) 510-G,a pair of edge cloud nodes (ECNs) 520-1 and 520-2 (collectively, ECNs520), and a management system (MS) 530. It will be appreciated that,although only two ECNs 520 are depicted, fewer or more ECNs 520 may beused.

The GMB 510-G includes a global event dispatcher (GED) 511-G, a set ofglobal event queues (GEQs) 512 (collectively, GEQs 512), and a queuemonitor (QM) 513.

The ECNs 520 each include a local message bus (LMB) 521 (illustratively,ECN 520-1 includes an LMB 521-1 and ECN 520-2 includes an LMB 521-2) anda respective plurality of hosts 525 (illustratively, ENC 520-1 includesa plurality of hosts 525-11-525-1N and ECN 520-2 includes a plurality ofhosts 525-21-525-2M). The LMBs 521 each include a local event dispatcher(LED) 522 (illustratively, LMB 521-1 includes an LED 522-1 and LMB 521-2includes an LED 522-2) and a set of local event queues (LEQs) 523(illustratively, LMB 521-1 includes a set of LEQs 523-1 and LMB 521-2includes a set of LEQ 523-2).

The MS 530 includes a function manager 531. It will be appreciated thatthe MS 530 may be configured to include various other types of managerswhich may provide various other types of functions.

The GED 511-G is configured to receive events and dispatch the events tothe GEQs 512 for storage in the GEQs 512 while the events await transferto the LMBs 521 of the ECNs 520 and, eventually, processing by the hosts525 of the ECNs 520. The GED 511-G may be configured to determinequeuing of events in the GEQs 512 based on event type information of theevents that are received. The GED 511-G may be configured to determinequeuing of events in the GEQs 512 based on queue status information ofthe GEQs 512 that is received from the QM 513 (e.g., queue lengths,event arrival rates, event departure rates, or the like, as well asvarious combinations thereof). The operation of the GED 511-G indispatching events to the GEQs 512 may be similar to the operation of ED211 in dispatching events to the EQs 212 (presented with respect to FIG.2).

The GEQs 512 are configured to receive events from the GED 511-G and tostore the events while the events await transfer to the LMBs 521 of theECNs 520 and, eventually, processing by hosts 525 of the ECNs 520. TheGEQs 512, as presented in FIG. 5, may be configured to allow foraddressing based on event type. Namely, the set of GEQs 512 includes,for each of the event types, a respective GEQ 512 for the respectiveevent type (illustratively, the GMB 511-G includes a GEQ 512-1 thatstores events of event type A and a GEQ 512-1 that stores events ofevent type B). The GEQs 512, although omitted from FIG. 5, may beconfigured to allow for addressing based on a combination of event typeand edge cloud node (e.g., the set of GEQs 512 may include, for each ofthe event types, a respective GEQ 512 for each of the ECNs 520 (and,thus, for each of the LMBs 521 of the ECNs 520) that is subscribed tohandle events of that respective event type. The GEQs 512 are configuredto provide queued events to the LMBs 521 of the ECNs 520 responsive torequests from the LMBs 521 of the ECNs 520 (e.g., LMB 521-1 of ECN 520-1may request events of event type A from GEQ 512-1 and LMB 521-2 of ECN520-2 may request events of event type B from GEQ 512-2). It will beappreciated that, although primarily presented with respect to asituation in which each ECN 520 is only subscribed to handle events of asingle event type (namely, ECN 520-1 being subscribed to handle eventsof event type A and ECN 520-2 being subscribed to handle events of eventtype B), one or more of the ECNs 520 may be subscribed to handle eventsof a multiple event types.

The QM 513 is configured to monitor the GEQs 512 for use in supportinghandling of events (e.g., for supporting GED 511-G in controllingdistribution of events to the GEQs 512, for supporting FM 531 incontrolling scaling of the hosts 525 for supporting processing ofevents, or the like, as well as various combinations thereof). Theoperation of the QM 513 of GMB 511-G may be similar to the operation ofQM 213 of MB 210 (presented with respect to FIG. 2).

The ECNs 520 are configured to support queuing and processing of events.The events are queues by the LMBs 521 of the ECNs 520 and the events areprocessed by the hosts 525 of the ECNs 520.

The LMBs 521 of the ECNs 520 are configured to manage events that areawaiting processing by the hosts 525 of the ECNs 520, respectively. TheLMBs 521 of the ECNs 520 are configured to receive events that are to beprocessed by the hosts 525 of the ECNs 520 and to provide the events tothe hosts 525 of the ECNs 520 for processing by the hosts 525 of theECNs 520.

The LMBs 521 of the ECNs 520 are configured to subscribe to the GMB511-G in order to retrieve events from the GEQs 512 of the GMB 511-G(illustratively, the LMB 521-1 is subscribed to GMB 511-G for event typeA while the LMB 521-2 is subscribed to GMB 511-G for event type B). TheLMBs 521 of the ECNs 520 may be configured to subscribe to the GMB 511-Gin order to retrieve events from the GEQs 512 of the GMB 511-G under thecontrol of the FM 531 (e.g., based on a request or instruction for anECN 520 to support handling of events of the event type, based on arequest or instruction for one or more of the hosts 525 of an ECN 520 tosupport handling of events of the event type, or the like). Theoperation of the LMBs 521 of the ECNs 520 in pulling events from the GMB511-G may be similar to the operation of the hosts 220 in pulling eventsfrom the EQs 212 of the MB 210 (e.g., based on local policies of theECNs 520, based on local conditions at the ECNs 520, or the like, aswell as various combinations thereof).

The LEDs 522 of the LMBs 521 are configured to receive events from theGEQs 512 of the GMB 511-G and to dispatch the events to the LEQs 523 forstorage in the LEQs 523 while the events await transfer to the hosts 525of the ECNs 520 to be processed by the hosts 525 of the ECNs 520. TheLEDs 522 may be configured to determine queuing of events in the LEQs523 based on queue status information of the LEQs 523 (e.g., queuelengths, event arrival rates, event departure rates, or the like, aswell as various combinations thereof), host status informationassociated with hosts 525 subscribed to or otherwise associated with theLEDs 522, or the like, as well as various combinations thereof. Theoperation of the LEDs 522 in dispatching events to the LEQs 523 may besimilar to the operation of ED 211 in dispatching events to the EQs 212(presented with respect to FIG. 2).

The LEQs 523 are configured to receive events from the LEDs 522 and tostore the events while the events await transfer to the hosts 525 of theECNs 520 to be processed by the hosts 525 of the ECNs 520. The LEQs 523,as presented in FIG. 5, may be configured to allow for addressing basedon hosts 525. Namely, the set of LEQs 523 includes, for each of thehosts 525 subscribed to retrieve events from the LMB 521, a respectiveLEQ 523 for the respective host (illustratively, the LMB 521-1 of ECN520-1 includes a set of LEQs 523-1 that includes an LEQ 523-1 for host525-11 and an LEQ 523-1 for host 525-1N and the LMB 521-2 of ECN 520-2includes a set of LEQs 523-2 that includes an LEQ 523-2 for host525-21). The LEQs 523 are configured to provide queued events to thehosts 525 responsive to requests from the hosts 525 (e.g., host 525-11may request events of event type A from the LEQ 523-1 to which the host525-11 is subscribed, host 525-1N may request events of event type Afrom the LEQ 523-1 to which the host 525-1N is subscribed, and the host525-21 may request events of event type B from the LEQ 523-2 to whichthe host 525-21 is subscribed).

The host 525 are configured to support handing of events. The hosts 525may be configured to support configuration of the hosts 525 to supportevent handling (e.g., obtaining event processing functions forrespective event types to be supported by the respective hosts 525,subscribing to event types to be supported by the respective hosts 525,configuring the hosts 525 to be able to store events to be processed atthe hosts 525, or the like, as well as various combinations thereof),pull events from the LMBs 521 for event types supposed by the respectivehosts 525, queue the events pulled from the LMBs 521 for event typessupported by the respective hosts 525, and process the events pulledfrom the LMBs 521 for event types supported by the respective hosts 525.The details of the host 525 are omitted for purposes of clarity;however, it will be appreciated that the hosts 525 may be configured ina manner similar to the hosts 220 (presented with respect to FIG. 2). Itwill be appreciated that the operation of the hosts 525 may be similarto the operation of the hosts 220 (presented with respect to FIG. 2);however, rather than pulling events from a centralized message bus, thehosts 525 pull events based on a distributed message bus (e.g., pullingevents from local message buses of the distributed message bus where thelocal message buses pull events from the global message bus of thedistributed message bus).

The GMB 511-G and LMBs 521 cooperate to provide a distributed messagebus for the hosts 525. In the distributed message bus, events arehierarchically passed from the GMB 511-G to the LMBs 521.

The GMB 511-G may be configured to maintain a variable number of GEQs512 for an event type or a constant number of GEQs 512 for an event type(e.g., subsets of which may be mapped to different ECNs 520). Forexample, where the number of GEQs 512 is constant (e.g., assuming 10total queues) and events of event type A are only being handled by theECN 520-1 then, based on a decision to scale out handling of event typeA to ECN 520-2, the mapping of the ten GEQs 512 may be changed such thatx GEQs 512 are mapped to ECN 520-1 and 10-x GEQs 512 are mapped to ECN520-2. It is noted that this control over scaling of the GMB 511-G maybe provided by the FM 531 or other suitable element.

The LMBs 521 each may be configured to maintain a variable number ofLEQs 523 for an event type or a constant number of LEQs 523 for an eventtype (e.g., subsets of which may be mapped to different hosts 525 orsubsets of hosts 525). For example, where the number of LEQs 523-2 ofECN 520-2 is variable and events of event type B are only being handledby the host 525-21 of the ECN 520-2 then, based on a decision to scaleout handling of event type B to host 525-2M of ECN 520-2, the set ofLEQs 512 may be changed such that an additional LEQ 523-2 isinstantiated on LMB 521-2 of ECN 520-2 for host 525-2M. It is noted thatthis control over scaling of the LMB 521 may be provided locally at theECN 520-2.

The ECNs 520 may be configured to control configuration and scaling ofthe hosts 525, for supporting processing of events, locally within theECNs 520, respectively. The ECNs 520 may be configured to controlconfiguration of the hosts 525 of the ECNs 520 for supporting processingof events (e.g., requesting or instructing hosts 525 to obtain eventprocessing functions for particular event types, to subscribe to LMBs521 for particular event types, or the like, as well as variouscombinations thereof). The scaling may include scale out or scale in.The scaling of hosts 525 may include configuration of existing hosts525, instantiation of new hosts 525, termination of existing hosts 525,or the like, as well as various combinations thereof. The localizedoperation of each of the ECNs 520 in controlling configuration andscaling of the respective hosts 525 of the ECNs 520, for supportingprocessing of events by the respective hosts 525 of the ECNs 520, may besimilar to the operation of the FM 230 in controlling configuration andscaling of the hosts 220 for supporting processing of events (presentedin FIG. 2).

The FM 531 is configured to control deployment of event processingfunctions to ECNs 520. The FM 531 may be configured to control thedeployment of event processing functions to ECNs 520 based oninformation from the QM 513. The FM 531 may be configured to supportconfiguration and scaling of the hosts 525 for supporting processing ofevents (e.g., requesting or instructing hosts 525 to obtain eventprocessing functions for particular event types, to subscribe to LMBs521 for particular event types, or the like, as well as variouscombinations thereof) if centralized control over configuration andscaling of the hosts 525 is to be used in addition to localized controlover configuration and scaling of the hosts 525 by the respective ECNs520. The FM 531 is configured to provide various other managementfunctions.

It will be appreciated that the event handling system 500, althoughprimarily presented as being organized in a particular manner, may beorganized in various other ways (e.g., using other numbers, types, orarrangements of hosts or host capabilities, message bus capabilities, orthe like, as well as various combinations thereof).

Various embodiments of the event handling capability, as discussedabove, may be configured to solve various problems associated withhandling of events for a service or application in a distributed eventhandling system.

Various embodiments of the event handling capability may be configuredto support event handling based on distribution of informationcollection and decision making between the hosts and a message busincluding a global message queue that supports the hosts. The individualbehaviors of the hosts are reflected in the status and the dynamics ofthe queues in the message bus, manifesting in different arrival anddeparture rates and backlogs of the individual queues. This informationis available to various elements of the system and may be used forsolving various problems as discussed herein.

Various embodiments of the event handling capability may be configuredto solve a first problem of determining scaling (e.g., scale up andscale down) of the number of hosts participating in the event handlingfor the service or application in the distributed event handling system.In general, only hosts that have the software for the service orapplication can support the service or application and execute functionsfor the service or application. Installing software for the service orapplication generally consumes small, but non-negligible, amount ofresources in the event handling system. As such, installing software forall services or applications on every host is not feasible, however,limiting the installation of software to too few hosts limits the amountof resources that are available for the service or application (whichcan lead to degradation of performance of the service or application(e.g., jitter in latency) and, thus, a decrease in quality-of-experience(QoE) of the end users). In view of such competing considerations,selecting the appropriate number of hosts on which software for theservice or application is to be installed may be challenging. In atleast some embodiments, this first problem may be solved by (1)considering the backlog and the changes in backlog of the queues in themessage bus of a particular event type and (2) initiating scaling forthe event type based on the queue status information where the scalingmay include scale out (e.g., if the queues for a particular event arebacklogged and draining relatively slowly then this is taken as anindicator to request installation of the corresponding functions on anadditional host to increase the processing capacity (which will increasethe performance of the service or application for which the event typeis supposed) or scale in (e.g., if the queues for a particular eventtype are lightly loaded and drain relatively quickly then this is takenan indicator to request that the function be uninstalled from one (orseveral) hosts). It will be appreciated that various other embodimentspresented herein may solve or contribute to solving the first problem.

Various embodiments of the event handling capability may be configuredto solve a second problem of determining distribution of events of theservice or application to hosts that support the service or applicationin the distributed event handling system. In general, the distributionof events of the service or application to hosts that support theservice or application should be determined such that none of the hostsare overloaded and such that the hosts have the resources needed toprocess events efficiently. However, since hosts may support multipleservices or applications, the resource availability at the hosts forevent processing may depend on the workloads of the various services orapplications supported by the hosts (which may vary over time). In viewof such competing considerations, determining distribution of events ofthe service or application to hosts that support the service orapplication may be challenging. In at least some embodiments, thissecond problem may be solved by (1) considering the backlog and thechanges in backlog of the queues in the message bus of a particularevent type by calculating a score on these two metrics for each queuewhere the score increases as the conditions of a queue status improve(e.g., decreasing queue length and/or increasing drain rate) and (2)dispatching incoming events to the queue that has the highest score(which will minimize the latencies for the corresponding service orapplication for which events of the event type are being handled). Itwill be appreciated that various other embodiments presented herein maysolve or contribute to solving the second problem.

Various embodiments of the event handling capability may provide variousother advantages or potential advantages.

FIG. 6 depicts a high-level block diagram of a computer suitable for usein performing various functions described herein.

The computer 600 includes a processor 602 (e.g., a central processingunit (CPU), a processor having a set of one or more processor cores, orthe like) and a memory 604 (e.g., a random access memory (RAM), a readonly memory (ROM), or the like). The processor 602 and the memory 604are communicatively connected.

The computer 600 also may include a cooperating element 605. Thecooperating element 605 may be a hardware device. The cooperatingelement 605 may be a process that can be loaded into the memory 604 andexecuted by the processor 602 to implement functions as discussed herein(in which case, for example, the cooperating element 605 (includingassociated data structures) can be stored on a non-transitorycomputer-readable storage medium, such as a storage device or otherstorage element (e.g., a magnetic drive, an optical drive, or thelike)).

The computer 600 also may include one or more input/output devices 606.The input/output devices 606 may include one or more of a user inputdevice (e.g., a keyboard, a keypad, a mouse, a microphone, a camera, orthe like), a user output device (e.g., a display, a speaker, or thelike), one or more network communication devices or elements (e.g., aninput port, an output port, a receiver, a transmitter, a transceiver, orthe like), one or more storage devices or elements (e.g., a tape drive,a floppy drive, a hard disk drive, a compact disk drive, or the like),or the like, as well as various combinations thereof.

It will be appreciated that computer 600 of FIG. 6 may represent ageneral architecture and functionality suitable for implementingfunctional elements described herein, portions of functional elementsdescribed herein, or the like, as well as various combinations thereof.For example, computer 600 may provide a general architecture andfunctionality that is suitable for implementing one or more of anelement of CN 110, a host 120 or a portion thereof, the MS 130 or aportion thereof, the MB 131 or a portion thereof, the FM 132 or aportion thereof, the MB 210 or a portion thereof, a host 220 or aportion thereof, the FM 230 or a portion thereof, GMB 511-G or a portionthereof, an ECN 520 or a portion thereof, an LED 521 or a portionthereof, a host 525 or a portion thereof, the MS 530 or a portionthereof, or the like, as well as various combinations thereof.

It will be appreciated that the functions depicted and described hereinmay be implemented in software (e.g., via implementation of software onone or more processors, for executing on a general purpose computer(e.g., via execution by one or more processors) so as to provide aspecial purpose computer, and the like) and/or may be implemented inhardware (e.g., using a general purpose computer, one or moreapplication specific integrated circuits (ASIC), and/or any otherhardware equivalents). It will be appreciated that at least some of thefunctions discussed herein as software methods may be implemented withinhardware, for example, as circuitry that cooperates with the processorto perform various functions. Portions of the functions/elementsdescribed herein may be implemented as a computer program productwherein computer instructions, when processed by a computer, adapt theoperation of the computer such that the methods and/or techniquesdescribed herein are invoked or otherwise provided. Instructions forinvoking the various methods may be stored in fixed or removable media(e.g., non-transitory computer-readable media), transmitted via a datastream in a broadcast or other signal bearing medium, and/or storedwithin a memory within a computing device operating according to theinstructions.

It will be appreciated that the term “or” as used herein refers to anon-exclusive “or” unless otherwise indicated (e.g., use of “or else” or“or in the alternative”).

It will be appreciated that, although various embodiments whichincorporate the teachings presented herein have been shown and describedin detail herein, those skilled in the art can readily devise many othervaried embodiments that still incorporate these teachings.

What is claimed is:
 1. An apparatus configured to support handling ofevents by a message bus of an event handling system, the apparatuscomprising: a processor and a memory communicatively connected to theprocessor, the processor configured to: maintain, by the message bus foran event type, a respective set of event queues for the event type,wherein the event queues for the event type are associated withrespective ones of a set of hosts subscribed to the message bus for theevent type; receive, by the message bus for the event type, an event ofthe event type that is published to the message bus; store, by themessage bus, the event of the event type in one of the event queues forthe event type based on respective sets of queue status informationassociated with the respective event queues; and send, by the messagebus, the event of the event type toward one of the hosts subscribed tothe message bus for the event type based on a request from the one ofthe hosts subscribed to the message bus for the event type.
 2. Theapparatus of claim 1, wherein the processor is configured to:instantiate the respective event queues for the event type based onrespective requests by the respective hosts to subscribe to the messagebus for the event type.
 3. The apparatus of claim 1, wherein, for atleast one of the event queues, the respective set of queue statusinformation comprises at least one of a queue length of the respectiveevent queue, an event arrival rate of the respective event queue, or anevent departure rate of the respective event queue.
 4. The apparatus ofclaim 1, wherein the processor is configured to: compute, for each ofthe event queues based on the respective sets of queue statusinformation associated with the respective event queues, a respectivequeue score for the respective event queue.
 5. The apparatus of claim 4,wherein the respective queue scores for the respective event queues areconfigured to enable selection of a longer one of the event queues overa shorter one of the event queues, for storing events of the event type,based on an indication that a length of the longer one of the eventqueues and a length of the shorter one of the event queues are changingat different rates.
 6. The apparatus of claim 4, wherein the respectivequeue score of the respective event queue is based on an exponentiallyweighted moving average of a queue length of the respective event queueand an exponentially weighted moving average of a departure rate of therespective event queue.
 7. The apparatus of claim 1, wherein theprocessor is configured to: terminate the respective event queues forthe event type based on respective requests by the respective hosts tounsubscribe from the message bus for the event type.
 8. The apparatus ofclaim 1, wherein the processor is configured to: send, toward a functionmanager configured to support scaling of hosts within the event handlingsystem, the respective queue status information of the respective eventqueues.
 9. The apparatus of claim 1, wherein the processor is configuredto: send, toward a function manager configured to support scaling ofhosts within the event handling system, per-host queue statusinformation of the host determined based on the respective queue statusinformation of the respective event queue associated with the host andbased on queue status information of a second event queue associatedwith the host for a second event type.
 10. A method for handling ofevents by a message bus of an event handling system, the methodcomprising: maintaining, by the message bus for an event type, arespective set of event queues for the event type, wherein the eventqueues for the event type are associated with respective ones of a setof hosts subscribed to the message bus for the event type; receiving, bythe message bus for the event type, an event of the event type that ispublished to the message bus; storing, by the message bus, the event ofthe event type in one of the event queues for the event type based onrespective sets of queue status information associated with therespective event queues; and sending, by the message bus, the event ofthe event type toward one of the hosts subscribed to the message bus forthe event type based on a request from the one of the hosts subscribedto the message bus for the event type.
 11. An apparatus, comprising: aprocessor and a memory communicatively connected to the processor, theprocessor and the memory configured to support a message bus of an eventhandling system, the message bus comprising: a set of event queues foran event type supported by the event handling system, wherein the eventqueues for the event type are configured to store events for respectiveones of a set of hosts subscribed to the message bus for the event type;a queue monitoring element configured to monitor the event queues and todetermine, for each of the event queues, respective queue statusinformation associated with the respective event queue; and an eventdispatch element configured to receive an event of the event type thatis published to the message bus and to dispatch the event of the eventtype to one of the event queues for the event type based on therespective queue status information associated with the respective eventqueues; wherein the message bus is configured to send the event of theevent type toward one of the hosts subscribed to the message bus for theevent type based on a request from the one of the hosts subscribed tothe message bus for the event type.
 12. An apparatus configured tosupport handling of events by a host of an event handling system, theapparatus comprising: a processor and a memory communicatively connectedto the processor, the processor configured to: subscribe, by the host,to a first event queue of a message bus, the first event queue of themessage bus configured to store events of a first event type to beprocessed by a first event processing function of the host; subscribe,by the host, to a second event queue of the message bus, the secondevent queue configured to store events of a second event type to beprocessed by a second event processing function of the host; maintain,by the host, a local buffer configured to store events received from thefirst event queue of the message bus and events received from the secondevent queue of the message bus; and retrieve, by the host based on alocal queuing policy of the host and a local event retrieval conditiondetected at the host, a retrieved event comprising a first event fromthe first event queue of the message bus or a second event from thesecond event queue of the message bus.
 13. The apparatus of claim 12,wherein the processor is configured to subscribe to the first eventqueue of the message bus based on a determination that the host supportsthe first event processing function.
 14. The apparatus of claim 12,wherein the processor is configured to subscribe to the second eventqueue of the message bus based on a determination that the host supportsthe second event processing function.
 15. The apparatus of claim 12,wherein the processor is configured receive scaling requests from afunction manager, wherein the processor is configured to subscribe tothe first event queue of the message bus based on a first request fromthe function manager and to subscribe to the second event queue of themessage bus based on a second request from the function manager.
 16. Theapparatus of claim 12, wherein the local buffer of the host comprises afirst host event queue configured to store events received from thefirst event queue of the message bus and a second host event queueconfigured to store events received from the second event queue of themessage bus.
 17. The apparatus of claim 12, wherein the local buffer ofthe host comprises a first-in-first-out buffer configured to storeevents received from the first event queue of the message bus and eventsreceived from the second event queue of the message bus.
 18. Theapparatus of claim 12, wherein the processor is configured to: select,by the host from the local buffer configured to store events receivedfrom the first event queue of the message bus and events received fromthe second event queue of the message bus based on a local eventselection condition detected at the host, a selected event; and processthe selected event.
 19. The apparatus of claim 18, wherein the selectedevent is an event of the first event type, wherein the selected event isprocessed by the host using the first event processing function of thehost.
 20. The apparatus of claim 18, wherein the selected event is anevent of the second event type, wherein the selected event is processedby the host using the second event processing function of the host. 21.The apparatus of claim 12, wherein the processor is configured to:detect a request for the host to stop handling events of the first eventtype; unsubscribe from the first event queue of the message bus based onthe request for the host to stop handling events of the first eventtype; process, by the host using the first event processing function ofthe host, any events of the local buffer of the host of the first eventtype; and initiate removal of the first event processing function fromthe host.
 22. The apparatus of claim 12, wherein the processor isconfigured to: detect a request for the host to stop handling events ofthe second event type; unsubscribe from the second event queue of themessage bus based on the request for the host to stop handling events ofthe second event type; process, by the host using the second eventprocessing function of the host, any events of the local buffer of thehost of the second event type; and initiate removal of the second eventprocessing function from the host.
 23. A method to support handling ofevents by a host of an event handling system, the method comprising:subscribing, by the host, to a first event queue of a message bus, thefirst event queue of the message bus configured to store events of afirst event type to be processed by a first event processing function ofthe host; subscribing, by the host, to a second event queue of themessage bus, the second event queue configured to store events of asecond event type to be processed by a second event processing functionof the host; maintaining, by the host, a local buffer configured tostore events received from the first event queue of the message bus andevents received from the second event queue of the message bus; andretrieving, by the host based on a local queuing policy of the host anda local event retrieval condition detected at the host, a retrievedevent comprising a first event from the first event queue of the messagebus or a second event from the second event queue of the message bus.